1. Field of the Invention
The invention relates to an automatic levelling device for a vehicle seat, having at least one linearly working drive means operatively connected on the one hand to the vehicle seat, which is pivotable relative to the vehicle about at least one axis, and on the other hand to the vehicle, and having at least one detecting means for detecting the position of the seat relative to the horizontal plane, the detecting means, when the seat deviates from the horizontal plane, delivering a signal to the drive means for returning the seat to the horizontal position.
2. Discussion of Background and Relevant Information
Devices of the kind indicated above are primarily used for driver's seat in tractors and other construction or working vehicles and cross-country vehicles. The purpose thereof is above all to prevent back-injuries and pain in the back for the driver of such vehicles when driving over rough terrain, for instance for the driver of a tractor during plowing when one of the wheels of the tractor runs on unplowed ground and the other wheel runs in a plowed furrow. Should the driver's seat be fixed in such a situation this would mean that the body of the driver would be inclined or tilted, which might lead to the above-mentioned trouble, especially if the ground is also rough so that the driver is constantly subjected to jolts and vibrations in such a position. Apart from this, a device of the above described kind also permits a much more comfortable driving position which enhances the capability of manoeuvering the vehicle, for instance when driving on a bank.
Devices of the kind indicated above are previously known through for instance U.S. Pat. Nos. 3,315,934 and 3,021,107, wherein fluid operated cylinders are used as drive means. The fluid operated cylinders are provided substantially vertically on each side of the pivot axis of the pivotal connection between the vehicle seat and the vehicle. In order to control the drive means in such a way that it restores the horizontal position of the seat when the vehicle is inclined, both these prior art devices employ a valve having an inertia sensitive valve member therein for detecting the lateral inclination.
These known solutions have the disadvantage that the devices are relatively bulky, especially due to the positioning of the drive means, and thus occupy an unnecessarily large-portion of the normally narrow space at the driver's seat of a vehicle of the kind in question, and may even be impossible to install on an existing vehicle, due to lack of space.
Another disadvantage of these prior art devices lies in the fact that they employ hydraulic drive means intended to be supplied from the normal hydraulic system of the vehicle. The disadvantage of this solution is primarily that an operation of the levelling device under unfortunate circumstances may lead to a pressure drop in the hydraulic system of the vehicle so that this can not adequately supply other vital devices connected to the hydraulic system, with the result that the operation of these devices may be obstructed in such a case. Furthermore special measures will have to be taken for reliable drawing of the hydraulic lines so that there is no danger of crushing or pulling loose the same. Finally, there is always a danger of leakage at the connection of the hydraulic lines, at the control valve or at the drive means themselves, and such a leakage is absolutely not desirable adjacent the driver's seat.
U.S. Pat. No. 2,966,937 does disclose a device of the kind described in the introduction, which employs electrical motors for adjusting the position of the seat. However, this known device also suffers from the disadvantage of being bulky, in this case especially in its height. In detail this device employs rotary drive means which through a screw and worm gear operate a threaded rod vertically positioned between the vehicle seat and the vehicle for adjusting the position of the vehicle seat when being driven up and down. Thus, this known device requires that a relatively large vertical space be available at the driver's stand so that the adjusting apparatus can be mounted between the seat and the vehicle without unduly restricting the remaining space above the seat. This means that the known device cannot be used for subsequent installment in driving compartments on existing vehicles where the vertical space is already restricted.
Finally, the device according to U.S. Pat. No. 2,966,937 is relatively complex and employs a great number of movable parts requiring machining. Due to this fact the complete device is also relatively expensive.